1. Field of the Invention
The invention relates to a lamp. More particularly, the invention relates to a light emitting diode (LED) lamp that has a heat dissipation module.
2. Description of Related Art
An LED is a semiconductor element, and a material of a light emitting chip of the LED mainly includes a compound selected from groups III-V chemical elements, such as gallium phosphide (GaP) or gallium arsenide (GaAs). The light emitting principle of the LED lies in the conversion of electric energy into light. Specifically, after a current is applied to the compound semiconductor, the LED releases an excess of energy in a form of light through the combination of electrons and electron holes. Since the luminance of the LED does not result from thermal emission or electric discharge, the life span of the LED could reach 100,000 hours or more. Moreover, the LED has the advantages of fast response speed, compact size, low power consumption, low pollution, high reliability, capability for mass production, etc. Therefore, the application of LED is fairly extensive. For instance, the LED could be applied to a mega-size outdoor display board, a traffic light, a mobile phone, a light source of a scanner and facsimile machine, an LED lamp, and so forth.
In general, the LED lamp requires optical elements (e.g., a prism) for achieving light-condensing effects. However, excessive elements lead to the difficulty in assembly and the increase in manufacturing costs, and the thickness of the lamp could not be effectively reduced. From another perspective, in order to prevent the LED from being overheated when the LED emits light, a heat dissipation structure could be configured in the LED lamp for heat dissipation. The larger the heat dissipation area of the heat dissipation structure, the greater the heat dissipation performance. Hence, how to expand the heat dissipation area of the heat dissipation structure becomes an important topic in this industry.
U.S. Pat. Nos. 7,290,902 and 7,025,482 both disclose a direct-type illumination device in which a circular light guide plate (LGP) has concentric annular trenches. U.S. Pat. No. 4,105,293 discloses an LED light source that surrounds a circular LGP. Taiwan Patent No. TW 1329182 discloses a lamp in which an LED surrounds a seat, a bowl-shaped LGP covers the seat, and heat dissipation fins surround an outer surface of a lampshade.